Approximately 800,000 people in the US suffer a stroke each year, of which approximately 660,000 (83%) survive. Of the surviving population, studies suggest approximately 60% (nearly 400,000) have lower extremity motor deficit in the acute stages of recovery. Of this population, studies suggest approximately half (i.e., 200,000) are unable to walk without assistance six months after the stroke. The inability to walk unassisted has an obvious impact on an individual's independence and community-dwelling capability, and thus quality of life. Similarly, impaired balance and compromised walking ability increase the incidence of falls and resulting fractures.
In an effort to improve mobility outcomes for the population of people with mobility deficit following stroke, body-weight-supported treadmill training (BWSTT) has been employed. In this intervention, a portion of a patient's body weight is suspended above a treadmill through an overhead suspension point, while one or more therapists manipulate portions of a patient's body, most commonly the lower limb, in order to emulate walking and thereby facilitate its recovery. A number of studies have been conducted investigating the efficacy of BWSTT for recovery after stroke, including. There is not general agreement in these studies regarding the efficacy of BWSTT, relative to conventional physical therapy interventions, although a number suggest that BWSTT provides no clear benefit relative to conventional therapy. In order to provide locomotor training similar to BWSTT with fewer therapists and perhaps greater consistency, robotic versions of BWSTT have been developed, which maintain the treadmill and overhead body weight suspension system, but replace the manual manipulation of the legs with robotic manipulation. Like manually-assisted (MA) BWSTT, robotic-assisted (RA) BWSTT systems have also been the subject of recent studies comparing their efficacy to conventional therapy. Like the MA-BWSTT studies, there is not general agreement regarding efficacy, although several studies suggest that the benefits of RA-BWSTT relative to conventional therapy are not clear.
BWSTT interventions offer little static or dynamic balance training. In the case of RA-BWSTT, the need for balance is nearly fully removed from the locomotion activity, while in the case of MA-BWSTT, the need for balance is largely absent. In both cases, overhead body-weight support is a substantially stabilizing effect, and in the specific case of the RA-BWSTT, trunk movement is kinematically constrained along a reduced set of movement axes. The presence of substantially stabilizing forces, in addition to kinematic constraints, significantly impedes the development of balance during such training.
The fact that balance is not required for BWSTT is in fact a substantial asset in early phases of therapeutic intervention for gait retraining. Most people in the rehabilitation community agree that early intervention can provide substantive therapeutic benefits, and many contend that BWSTT systems enable earlier therapeutic intervention than would otherwise be possible with conventional therapy. Despite this, as patients develop increased strength, the artificial stabilization present in the BWSTT interventions impedes the retraining of balance, which by necessity involves movement of the body in space, unimpeded movement of the trunk and upper and lower limbs, and proper placement of each foot to ensure dynamic stability. Integrating and coordinating these movements with the vestibular and proprioceptive systems, in accordance with the physics (i.e., dynamics) of locomotion, is a learned response that is essential to safe walking.